| Summary: | The main theme of the study was to determine long-term temporal and spatial patterns of the nutrient regime [total phosphorus (TP) and total nitrogen (TN)], chlorophyll dynamics (CHL), suspended solids, biological oxygen demand, chemical oxygen demand, total organic carbon, and electrical conductivity in Yeongsan watershed, based on the data set of 10 years (2007–2016) and then to develop the nutrient–chlorophyll empirical models. Summer monsoon is the key determinant which regulates the nutrient concentrations and algal growth of the watershed. The nutrient concentrations (TP and TN) were greater in headwater zone (Hz) compared to midwater zone (Mz) and downwater zone (Dz) because of high flushing rate during monsoon season. TP (R2 = 0.23, p < 0.01) is the key regulating factor for algal growth compared to TN (R2 = 0.03, p < 0.01). The concentration of nutrients (TP and TN) was more influenced by the inflow and outflow in the Hz and Dz. Analysis of trophic state index deviation indicated that phosphorus limitation was severe in Hz, Mz, and Dz, and biogenic turbidity was also observed in the watershed. The chemical health analysis of the Yeongsan watershed suggested that the overall chemical health was categorized as a Good to Excellent condition.
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